1. Field of the Invention
The invention relates to an electrochemical storage cell or battery of the alkali metal and chalcogen type with at least one anode space to contain an alkali metal as the anolyte and a cathode space intended for receiving the catholyte, which are separated from each other by an alkali-ion-conducting solid electrolyte wall, and that sulfur or sulfides are filled into the cathode space.
2. Description of the Prior Art
Such rechargeable electrochemical storage cells with a solid electrolyte are highly suited for the construction of storage batteries of higher energy and power density. The electrolyte of beta aluminum oxide, used for instance, in sodium/sulfur storage cells, passes only sodium ions. In contrast to the lead storage cell, this means that practically no discharge and no secondary reactions occur during this charge, such as, for instance, water dissociation in the lead-lead-oxide system. The current yield, i.e. the Faraday efficiency of a sodium/sulfur storage cell is near 100%.
However, it is an important disadvantage in such a storage cell that, with large currents, it can be only partially recharged. In the case of Na/S storage cells, this disadvantage is connected with the fact that sulfur (with small percentages of dissolved Na.sub.2 S.sub.5) and Na.sub.2 S.sub.5 (with percentages of dissolved sulfur) form two immiscible liquids at the operating temperature of such a storage cell, which is 300.degree. to 350.degree. C. For, if a discharged sodium/sulfur storage cell, which contains Na.sub.2 S.sub.3 in the cathode space is recharged again, sulfides containing more sulfur are first formed until Na.sub.2 S.sub.5 has been produced in the cathode space or at least locally. Upon further recharging, liquid sulfur is then formed at points with very active electrochemical reaction. This liquid sulfur being an insulator, blocks the electrochemical processes at that point. In order to avoid this disadvantage, a carbon or graphite felt is filled into the cathode space in addition to the sulfur, as is known from German Published Non-Prosecuted Application No. 2 754 454. This felt is provided with a porous layer of an alkali-ion-conducting substance which leaves the surface of its fibers free in the manner of islands.
While improved rechargeability of the storage cell is achieved with these measures, the desired values are not yet achieved thereby.